Modern Concept Science and Technology 9

Modern Concept Science and Technology NOVA Science Book 9 147Newton’s laws of motionSir Isaac Newton was an English physicist and mathematician. He put forward three laws of motion in 1686 which are known as Newton’s laws of motion. Newton’s first law of motion gives a precise definition of force and inertia. The second law of motion describes the relation of acceleration of a body with the force applied and mass of the body. Newton’s third law of motion establishes the relationship between ‘action’ and ‘reaction’ forces.Newton’s First Law of MotionGalileo was the first to establish that no force is required to keep a body moving uniformly along a straight line. Unbalanced force is required for changing the state or direction of motion of the body. The equal force acting in the opposite direction, which does not change the state of rest or uniform motion of an object, is known as balanced forces. A body under the action of balanced forces does not change its position of rest or uniform motion. The unequal and opposite forces acting on a body, which change its state of rest or uniform motion are called unbalanced forces. Unbalanced forces acting on a body can change its state of rest or uniform motion.Statement: Every body continues to be in its state of rest or of uniform motion along a straight line unless it is acted upon by an external force.Newton’s first law of motion consists of three parts.i. The first part- A body at rest remains at rest unless some external force acts on it to change its state of rest. For example, a football on the ground remains in a state of rest unless a player kicks it.ii. The second part- A body in uniform motion continues to move uniformly in a straight line unless some external force acts on it to change its state of motion. For example, to stop a moving car, brakes must be applied.iii. The third part- A body continues to move along the same straight line unless some external force acts on it. For example, to turn a car moving over a straight road, we have to apply a force on the steering wheel of the car.Fact and ReasonNewton’s first law of motion is also called the law of inertia.Newton’s first law of motion states that every body resists the change in its state of rest or that of uniform motion. Such property of a body is known as inertia. Therefore, Newton’s first law of motion is also called the law of inertia.

148 NOVA Science Book 9 Modern Concept Science and TechnologyApplication of Newton’s first law of motioni. Drivers use the seat belt to prevent forward fall while using emergency break.ii. A person jumping out from a moving bus falls forward and gets injured.iii. A rotating fan continues rotating for a while although the switch is turned off.iv. A book on the table remains in rest until and unless we displace or remove it.v. When a bullet is fired on a glass pane window, it makes a clean hole withoutcausing cracks in the glass.Newton’s Second Law of MotionActivityTo observe relation between acceleration and force.To observe relation between acceleration and mass.Take a football on the ground. Kick it with once with little force. The next time kick it with a greater force. Observe the acceleration in each of the two cases. Do you observe more acceleration when the ball is kicked with a greater force?Hold a tennis ball and a cricket ball. One after another, throw them on the ground with equal force. Observe the acceleration of each of the two balls. Do you observe more acceleration of tennis balls?We need more force to move an object faster. It means that the acceleration produced on a body is directly proportional to the force applied to it. A lighter object can be thrown faster but it is difficult to throw a heavier object as fast. A lighter object can be pushed faster than a heavier one. It means that the acceleration produced on a body is inversely proportional to its mass.Memory NoteThe second law of motion is the measurement of force.Acceleration produced on a body is directly proportional to the force applied to itAcceleration produced on a body isinversely proportional to its massWe apply more force from our muscles to speed up our motion.Our speed of running starts to decrease when we are given loads to carry with us.Vehicles are provided with an accelerator to apply more force by the engine to increase the speed.Cars can speed up faster on a road sloping upward than heavily loaded trucks.

Modern Concept Science and Technology NOVA Science Book 9 149Acceleration produced on a body is directly proportional to the force applied to itAcceleration produced on a body isinversely proportional to its massWe need to apply more force to carry a loaded cart.We need to apply more force to make an adult swing faster than that in the case of a baby in a swing.Statement: According to Newton’s second law of motion, ‘the acceleration produced on a body is directly proportional to the applied force and inversely proportional to the mass of the body (m).Mathematically,acceleration (a) α force (F) .................. (i) {When mass (m) remains constant}acceleration (a) α1mass (m) .........… (ii) {When the force applied (F) remains constant}Combining relation (i) and relation (ii), we geta α Fmor, F α maor, F = k ma ....... (iii) Where ‘k’ is a proportionality constant.When, m = 1 kg, a = 1 m/s2 then F = 1 N In such a condition, k = 1Substituting the value of ‘k’ in equation (iii), we getF = maMemory NoteOne newton is the amount of net force that gives an acceleration of 1 m/s² to a body with a mass of 1 kilogram.SOLVED NUMERICAL- 7.6A car of mass 1000 kg (along with passengers) is moving with a velocity of 72 km/h and it takes 2.5 s to stop it after the brakes are applied. Calculate the force exerted by the brakes on the car.SolutionHere, initial velocity of the car (u) = 72 km/hu = 72 × 100060 × 60 m/s = 20 m/sFinal velocity of the car (v) = 0 [since the car comes to rest]

150 NOVA Science Book 9 Modern Concept Science and TechnologyMass of the car (m) = 1000 kgTime taken to stop the car (t) = 2.5 sAccording to Newton’s second law of motion, force on the car is given by F = maor, = m(v – u)tor, = 1000(0 – 20)2.5 = – 200002.5∴ F = – 8000 NThe negative sign indicates that the force exerted by the brakes is opposite to the initial direction of acceleration of the car. It means car is decelerating.SOLVED NUMERICAL- 7.7A force of 500 N acts on a body of mass 1000 kg and the body is brought to rest within a distance of 64 m. Find the initial velocity and the time taken by the body to come to rest.SolutionHere, Force (F) = 500 NMass of the body (m) = 1000 kg Displacement (s) = 64 mAccording to Newton’s second law of motion, if F is the force applied on a body of mass ‘m’ to accelerate it with ‘a’.F = maa = Fm = 5001000 = 0.5 m/s2Since the body comes to rest by applying force on it. i.e. the body is retarding.So, final velocity (v) = 0Acceleration (a) = – 0.5 m/s²From the equation of motion,v² = u² + 2asor, 0 = u² + 2 × –0.5 × 64or, u² = 64or, u = 64 = 8 m/s

Modern Concept Science and Technology NOVA Science Book 9 151To calculate the time taken, use the equation of motionv = u + ator, 0 = 8 – 0.5 × tor 0.5 × t = 8∴ t = 16 s∴ initial velocity (u) = 8 m/s, time taken (t)=16 s and acceleration (a) = -0.5 m/s²Newton’s Third Law of MotionStatement: For every action, there is an equal and opposite reaction.When we kick a football, our foot exerts a forward force on the ball, but we also feel the force the ball exerts back on our foot. Whenever two bodies interact, the forces that they exert on each other are always equal in magnitude and opposite in direction. If a body A exerts a force F on a body B (an ‘action’), then B exerts aforce - F on A (a ‘reaction’). Mathematically, F A on B = - F B on AAction and reaction act on two different surfaces. Thus, they do not cancel each other.Fact and ReasonAction and reaction do not cancel each other even if they have equal magnitudes and opposite directions.When two equal and opposite forces act on the same body then the resultant force is zero. But action and reaction act on two different surfaces. Thus, they do not cancel each other.Some examples of newton’s third law of motion1. We need to press on the ground while walking. To start moving forward, we push backwards on the ground with our feet (action). As areaction, the ground pushes forward on ourfoot with a force of the same magnitude. This force accelerates our body forward.ABF B on AF A on BReaction: Floor pushes up and forwardAction: Foot pushes down and back

152 NOVA Science Book 9 Modern Concept Science and Technology2. Swimmers push water backward with their hands.While swimming, swimmers push water in a backward direction with their hands (action). Water also pushes the swimmer with equal force in the forward direction (reaction).3. A gun recoils while firing a bullet. When a bullet is fired from a gun, the forward force on the bullet (action) is equal to the force backward on the gun (reaction). Due to this backward force gun recoils.Fact and ReasonAn air-filled balloon goes upward on releasing its mouth, why? When the mouth of an air-filled balloon, which is in an upsidedown position, is released, the air inside rushes out downward (action). According to newton’s third law of motion, the air exerts an equal and opposite force on the balloon (reaction). The balloon goes upward (reaction).ActivityMake a balloon rocket: Take a longer ‘airship’ balloon, string, plastic straw, and tape. Insert the string inside a straw pipe and tie both the ends of the string to the rigid supports. Blow up the balloon and pinch its mouth. Tell your friend to tape the balloon to the straw. Finally, let the air come out of the balloon and observe the rocket fly. Discuss the principle behind the balloon rocket. Does the air pressure inside the balloon affect its flight? Discuss your finding in the classroom.Elasticity and PlasticityActivityPrepare clay for clay art. Also collect some other substances like toothpaste, eraser, scale, spring, etc. Then do the activities like pressing, twisting, stretching, etc. with each of them. Which substance obtains its original shape after removing force and which doesn’t? Categorise them into two groups. Discuss the results of your activity.Action ForceSwimmer pushes water in backward directionWater exerts a force on the swimmerReaction ForceForce on bullet(Action)Force on bullet(Reaction) Gun

Modern Concept Science and Technology NOVA Science Book 9 153Different types of external forces act on several bodies in our surroundings. Such external forces may produce a change in length, volume, and shape of the body. The external force which produces a change in length, volume, and shape of a body is called a deforming force. When a deforming force is applied to a body, which is not free to move, the shape or size of the body changes. A body whose shape is changed by a deforming force is called a deformed body.A relative displacement of particles takes place when an external force is applied to a body, which is not free to move. If the particles are displaced with a certain limit, they regain their original position after removing the deforming force. When the deforming force is removed, the body regains its original state due to the force developed with the body. Such a force developed within a body that restores the body into its original state is called restoring force. The property of a material to regain its original state when the deforming force is removed is called elasticity. The body which regains its original shape when the deforming force is removed is called an elastic body. The limit beyond which permanent deformation occurs in the object is called the elastic limit.Some Examples of ElasticityA body that completely regains its original shape and size after the removal of the deforming force is said to be perfectly elastic. There are no perfectly elastic bodies. Quartz fibre and Phosphor bronze are nearly perfectly elastic bodies.All matters don’t tend to regain their shape after removing force deforming them. For example, wet clay does not show any tendency to regain its original configuration after deformation. Perfectly wet clay is highly plastic. Bodies that do not return to their own shape and size after removing a deforming force is called plastic. Clay, semi-solid coal tar, wax, etc. are examples of nearly plastic bodies. Such bodies retain their deformed shape and size. The property of a body by which it tends to retain the altered shape and size on the removal of deforming force is called plasticity.Memory NoteThe bodies which partially regain their original form after removing a deforming force are called partially elastic. Actual bodies have elasticity in between the limits of perfect elasticity and perfect plasticity.

154 NOVA Science Book 9 Modern Concept Science and TechnologyFact and ReasonWhy are steel rods preferred for strong construction works?Steel is highly elastic. It has a high capacity to resist the deforming force. So, steel rods are used in the construction of strong buildings, bridges, etc.1. Force:Force is defined as the push or pull on a body that changes or tends to change the state of rest or uniform motion of a body in a straight line.2. Distance:The actual length of the path travelled by a moving body, irrespective of its direction is called the distance travelled by the body.3. Displacement: The shortest distance between the initial position and the final position of a moving body in a particular direction is called its displacement.4. Speed: The distance travelled by a body per unit time is called speed.5. Velocity: The distance travelled by a body per unit time in a particular direction is called its velocity.6. Uniform velocity: A body is said to have uniform velocity when it travels in a particular direction and covers equal distance in an equal interval of time.7. Non-uniform velocity: A body is said to have non-uniform velocity when it covers unequal distances in equal intervals of time.8. Average velocity: If the velocity of a body in a particular direction changes continuously at a uniform rate, then the arithmetic mean of the initial velocity and final velocity over a given period is called average velocity.9. Acceleration: The rate of change of velocity of a body with respect to time is called its acceleration.10. Positive acceleration: The rate of increase in velocity is called positive acceleration.11. Negative acceleration: The rate of decrease in velocity is called negative acceleration.12. Uniform acceleration: When a body travels in a straight line and its velocity changes by equal amounts in equal intervals of time, then it is said to have uniform acceleration.Terms and terminologies

Modern Concept Science and Technology NOVA Science Book 9 15513. Non-uniform acceleration: When the velocity of a body changes by unequal amounts in equal intervals of time, then it is said to have nonuniform acceleration.14. Displacement-time graph: The graphical relationship between the displacement of a body and the time taken is called the displacement-time graph.15. Velocity-time graph: The graphical relationship between the velocity of a body in motion and the time is called the velocity-time graph.16. Equation of motion: When a uniformly accelerated body travels in a straight line, then the relationship between the initial velocity (u), final velocity (v), distance travelled (s), acceleration (a), and time taken (t) is called the equation of motion.17. Inertia: The tendency of a body to remain in its state of rest or of uniform motion along a straight line is called inertia.18. Inertia of motion: The property of a body by which it resists any change in its state of uniform motion is called inertia of motion.19. Inertia of rest: The property of a body by which it resists any change in its state of rest is called inertia of rest.20. Newton’s first lawof motion: Everybody continues to be in its state of rest or of uniform motion along a straight line unless it is acted upon by an external force.21. Newton’s second law of motion: The acceleration produced on a body is directly proportional to the applied force and inversely proportional to the mass of the body (m).22. Newton’s third law of motion: For every action, there is an equal and opposite reaction.23. Deforming force: The external force which produces a change in length, volume, and shape of a body is called deforming force.24. Deformed body: A body whose shape is changed by a deforming force is called a deformed body.25. Restoring force: A force developed within a body that restores the body into its original state is called restoring force.26. Elasticity: The property of a material to regain its original state when the deforming force is removed is called elasticity.27. Elastic body: The body which regains its original shape when the deforming force is removed is called the elastic body.Terms and terminologies

156 NOVA Science Book 9 Modern Concept Science and Technology28. Perfectly elastic body: A body that completely regains its original shape and size after the removal of the deforming force is said to be perfectly elastic body.29. Plastic: Bodies that do not regain their original shapes when the deforming force is removed are called plastic.30. Perfectly plastic: Bodies that do not exhibit the property to return to their own shape and size after removing a deforming force are called perfectly plastic.31. Plasticity:The property of a body by which it tends to retain the altered shape and size on the removal of deforming force is called plasticity.32. Partially elastic: The bodies which partially regain their original form after removing a deforming force are called partially elastic.33. Elastic limit: The limit beyond which permanent deformation occurs in the object is called the elastic limit.Terms and terminologiesEXERCISESTEP 1 Multiple Choice Questions1. Choose the best answer from the given alternatives. a. What is distance? i. Length between two points ii. Meter iii. Rate of change of velocity iv. Direction b. Which one of the following are elastic objects?i. Steel, rubber, bow ii. Wax, coal tar, toothpaste iii. Steel, wax, spring iv. Rubber, toothpaste, clay c. How much force is required to produce an acceleration of 1 m/s2 on an object of mass 1 kg? i. 1 kg ii. 9.8 N iii. 1 N iv. 60 m d. Observe the given statement and arguments and select the best comment. Statement: When the driver applies brake, the passengers fall forward.

Modern Concept Science and Technology NOVA Science Book 9 157Argument 1: The inertia of rest makes them fall forward. Argument 2: The inertia of motion makes them fall forward. i. Statement and argument 1 are true. Argument 2 is false. ii. Statement and argument 2 are true. Argument 1 is false. iii. Statement is true. Arguments 1 and 2 are false. iv. Statement is false. Arguments 1 and 2 are true. e. Which of the following graphs represents uniform retardation?i. dtii. dtiii. vtiv. vtSTEP 2 Very Short Answer Type Questions2. Define the following terms. (a) Force (b) Distance (c) Displacement (d) Speed (e) Velocity (f) Uniform velocity (g) Non-uniform velocity (h) Average velocity (i) Acceleration (j) Positive acceleration (k) Negative acceleration (l) Displacement-time graph (m) Velocity-time graph (n) Equation of motion (o) Inertia (p) Inertia of motion (q) Inertia of rest (r) First law of motion(s) Second law of motion (t) Third law of motion (u) Elasticity(v) Plasticity (w) Elastic bodies (x) Elastic limit 3. Write the SI unit of speed and velocity. 4. Write a similarity between speed and velocity. 5. Match the following.1. Rate of increase in velocity a. Acceleration 2. The slope of the velocity-time graph b. Negative acceleration 3. The slope of displacement-time graph c. Positive acceleration 4. Rate of decrease in velocity d. Velocity 6. When swimming, the swimmer is using hands to push the water backwards. How does it help the swimmer? Explain based on the third law of motion. STEP 3 Short Answer Type Questions7. Write any two differences between: (a) Distance and Displacement

158 NOVA Science Book 9 Modern Concept Science and Technology(b) Speed and Velocity (c) Positive acceleration and Negative acceleration(d) s-t graph and v-t graph (e) Inertia of motion and Inertia of rest (f) Elasticity and Plasticity 8. Give suitable reason.(a) Velocity is a scalar quantity. (b) Acceleration of an object in uniform motion is zero. (c) When wind shakes the branch, the fruits break and fall. (d) When a moving bus applies brakes, passengers are thrown forward. (e) A gun recoils when a bullet is fired. 9. What type of motion does a particle have if its velocity-time graph is parallel to the time axis? 10. Name the type of inertia in each of the following cases:i. A passenger jumping out of a moving bus falls forward. ii. On taking a sharp turn, the driver falls sideways.iii. Dust particles are removed when a carpet is beaten with a stick.11. Identify the action-reaction forces in the following casesi. A boy walking on the ground. ii. Firing a bullet from the gun. iii. A book lying on a table. 12. A gun recoils on firing. Would it suffer greater or smaller recoil if the gun is heavy?13. A body is moving with a uniform acceleration of 2 m/s2. What does it mean?14. Derive the following equations of motion.a. v = u + at b. s = ut + 12 at2 c. v2 = u2 + 2as 15. Study the given news and answer the following questions. A supersonic aircraft called XB-1 flies faster than the sound. It travels at a velocity of 377.3 m/s. Questions An aircraft is travelling at a velocity of 377.3 m/s. What does it mean?

Modern Concept Science and Technology NOVA Science Book 9 15916. Study the given features and answer the following questions. Substances A and B can be squeezed. Substance A regains shape after the deforming force is removed, but substance B cannot.QuestionsWhich one of them is toothpaste? Which one of them is elastic? 17. Derive F = ma, where F is a force, m is a mass, and a is acceleration. 18. Observe the given diagram and answer the following questions.This is a suspension bridge made of steel. Why is steel chosen to make suspension bridges? Explain. STEP 4 Long Answer Type Questions19. Study the given concept map and answer the following questions. i. Who proposed the laws of motion? ii. Among A, B, and C, which one is the second law of motion?iii. Which one of them is used in launching a rocket? 20. The velocity-time graph of a ball moving on a surface is shown in the given figure. Calculate the force acting on the ball, if the ball has a mass of 100 g. 21. Answer the questions with the help of the given figure.i. Which parts of the graph represent the position of the car when it was at rest?ii. Which part of the graph represents the fastest speed?iii. Find the speed of the car between the region AB and FG.22. Study the given displacement-time graph and answer the following questions. i. Find the distance travelled by the bus.ii. What is the velocity of the bus in one second?iii. Calculate the average velocity of the bus. [Ans: 40 m, 7 m/s, 4 m/s] Laws of motionABCLawsInertiaMeasures the forceAction equals reactionFeatures20Velocity 10(in ms-1)Time (in s)0 1 2 3 416515013512010590756045301500 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300Time (in minutes)B CDE FGDistance (in Kilometres)403020100 2 4 6 8 10d(m)t(s)AB

160 NOVA Science Book 9 Modern Concept Science and TechnologyNumerical1. When the brake is applied in a vehicle travelling with a velocity of 25 m/s, the retardation becomes 0.5 m/s2. How far will it travel in 15 seconds? [Ans: 318.75 m]2. A bus is moving with a velocity of 72 km/h. On seeing the red traffic light, 27 m ahead on the road, the driver applied brakes, and the bus stopped at a distance of 25 m. Calculate the time taken by the car to come to rest. [Ans: 2.5 s]3. A bus is running with a velocity of 60 km/h. On seeing a child 11 m ahead on the road, the driver of the bus applied brakes, and the bus stopped at a distance of 10 meters. Calculate its retardation. [Ans: -13.89 m/s2]4. A vehicle that starts to move from rest gets an acceleration of 5 m/s2 within 2 seconds. Calculate the velocity and distance covered by the vehicle within the given time. [Ans: 10 m/s, 10 m]5. A force of 10 N acts on a body of mass 2 kg. If the body was initially at rest, calculate the velocity acquired by it in 5 s. [Ans: 25 m/s]6. The mass of a car along with its rider is 1,000 kg. It is moving with a velocity of 72 km/h and takes 5 seconds to stop after the brakes are applied. Calculate the retardation and retarding force exerted by the brakes on the car. [Ans: -4 m/s2, 4000 N]7. Find the force required to produce an acceleration of 2 m/s2 on a body of mass 10 kg. What would be its acceleration if the force was doubled? [ Ans: 20 N, 4 m/s2]8. A stone is dropped from the top of a building reaches the ground with a velocity of 49 ms-1. If the acceleration due to gravity is 9.8 ms-2, calculate the time for which the stone is falling freely. [Ans: 5 s] MCQ a b c d e Answer i i iii ii iii Take two balls, one with less mass and another with more mass, and roll them down a slope. Place a lightweight wooden slab in their path and observe the outcome. The lighter ball may stop upon hitting the slab, while the heavier ball may push it aside and continue moving. Conclude the relation between mass and inertia based on this practical work. PROJECT WORK

Modern Concept Science and Technology NOVA Science Book 9 161Dr. Shobhakar Dhakal is an expert in sustainable energy transition, climate change, and sustainable development. He is the head of the Department of Energy, Environment, and Climate Change at the Asian Institute of Technology. His research focuses on energy and climate change. He is involved in the Global Carbon Project. Dr. Shobhakar DhakalInspiring Nepalese Researcher“Give me a place to stand, and a lever long enough, and I will move the world.” — Archimedes. This is a famous quote from the scientist Archimedes. His quote captures the principle of the lever. He researched a lot on simple machines. He discovered the working mechanism of the lever. He made the Archimedes’ screw. He discovered the law of floatation. Questionsi. Archimedes claims that he can move the world. Which property of a simple machine does the quote represent?ii. Give a few examples of simple machines used in our daily lives. iii. Why do people use simple machines? iv. Are all machines around us simple machines?WARM UP ACTIVITYIntroductionA variety of tools are used in daily life to do our work. For example, sharp objects are used for cutting things, the pulley is used to lift loads, wheel and axle multiply effort or speed up our work, the slanted surface is used to multiply effort, etc. Such devices give us an advantage by changing the amount, speed, or direction of forces. The device which makes our work easier, faster, and more convenient is called a simple machine. For example, scissors, knife, nutcracker, bottle opener, spoon, pulley, screw, etc. These machines use muscular energy to work.SIMPLE MACHINEUNITESTIMATED TEACHING PERIODS8TH PR4 1

162 NOVA Science Book 9 Modern Concept Science and TechnologyScissors Beam balance Wheel barrow Pulley Screw AxeSome simple machinesActivityMake a list of compound machines. Identify the simple machines used in that machine and fill in a table as shown below:Compound machine Simple machines in use UseTerms Related to Simple MachinesLoad and Load DistanceLoad is the resistance to be overcome or the weight being lifted by a simple machine. SI unit of the load is newton (N). It is represented by ‘L’. The distance moved by the load in a simple machine is called load distance or load arm. Its SI unit is meter (m). It is represented by ‘Ld’.Effort and Effort DistanceThe effort is the force applied directly to a simple machine to move the load or to do work. SI unit of effort is newton (N). It is represented by ‘E’. The distance moved by effort applied in a simple machine is called effort distance or effort arm. Its SI unit is meter (m). It is represented by ‘Ed’.Mechanical Advantage (M.A)Mechanical advantage is a measure of the force amplification achieved by using a simple machine. The ratio of the load lifted to the effort applied in a simple machine is called mechanical advantage, i.e.MA = Load (L)Effort (E)Memory NoteA simple machine that multiplies force has a mechanical advantage greater than 1,(MA > 1).

Modern Concept Science and Technology NOVA Science Book 9 163MA doesn’t have units as it is a simple ratio of two forces.If the load lifted by the crowbar is 3 times greater than the effort applied, the mechanical advantage of a crowbar will be 3. It means that the crowbar multiplies the effort applied by 3 times.Fact and ReasonFriction should be reduced to increase the mechanical advantage of a machine, why?Weight and friction are the two factors that affect mechanical advantage. In a simple machine, the friction causes wastage of energy and reduces its MA. So, friction should be reduced to increase the mechanical advantage of a machine.Velocity Ratio (VR)Velocity ratio is the ratio of the velocity at which effort is applied on a machine to the velocity at which load moves. Velocity ratio is a measure that shows how many times the effort distance is longer than the load distance. Simply, the ratio of the distance moved by the effort to the distance moved by the load in a simple machine is called velocity ratio. i.e.VR = distance moved by effort (Ed)distance moved by load (Ld)VR doesn’t have units as it is a simple ratio of two distances.If the distance moved by effort is 4 times longer than the distance moved by load, velocity ratio of the simple machine will be 4. It means that the effort applied moves 4 times longer distance than the distance moved by load.Memory NoteWork done on a simple machine by a given effort is called input work. Input work = Effort (E) × Effort distance (Ed)Work done by a simple machine on the load is called output work. Output work = Load (L) × Load distance (Ld)Memory NoteFriction doesn’t affect effort distance and load distances. So, the velocity ratio isnot decreased friction.

164 NOVA Science Book 9 Modern Concept Science and TechnologyEfficiency (h)The ratio of output work to input work in a simple machine expressed as a percentage is called efficiency. i.e.Efficiency (h) = Output workInput work × 100%Efficiency doesn’t have a unit as it is a simple ratio of two works. If out of totaleffort applied in the crowbar, 75% is utilised to lift the load and 25% is wasted to overcome friction, then efficiency of a simple machine will be 75%.Fact and ReasonFriction should be reduced to increase the efficiency of a machine, why? Frictional force converts the applied energy in the simple machine into other forms of energy like heat. The efficiency of a machine decreases as the frictional force increases. Friction should be reduced to increase the efficiency of a machine.Relation Between MA, VR and EfficiencyThe efficiency of a simple machine is given by,Efficiency = Output workInput work × 100%or, Efficiency = Load × Load distanceEffort × Effort distance× 100%or, Efficiency = LoadEffortEffort distanceLoad distance× 100%or,∴ Efficiency = MAVR × 100%.Real or Practical MachineThe machine which has friction is called a real or practical machine.A real simple machine is never 100% efficient because of the following reasons:i. Friction affects the efficiency of a simple machine.ii. No machine is weightless and weight affects its efficiency.

Modern Concept Science and Technology NOVA Science Book 9 165Ideal or Perfect Simple MachineIn the case of an ideal simple machine, Input work = Output work, So, an ideal simple machine has 100% efficiency. A hypothetical frictionless machine in which total input work is converted into output work without wastage of energy is called an ideal or a perfect simple machine.Fact and ReasonAn ideal simple machine is a hypothetical concept.No machine can be weightless and frictionless, and total input work cannot be converted into output work without some wastage of energy. So an ideal simple machine is only a hypothetical concept.Types of Simple Machines1. Lever 2. Pulley 3. Wheel and axle4. Inclined plane 5. Wedge 6. ScrewPulleyPulley consists of a grooved disc with a rod passing through its centre to facilitate free rotation of the disc. A thread or cable over the groove is used to rotate the disc. The metallic or wooden circular disc having a groove along its rim and capable of rotating about an axis passing through its centre is called a pulley. Pulleys are an age-old simple machine and still of wide use in daily life. A common traditional use of pulleys is to lift buckets of water from the well. Nowadays several electrical devices, vehicles, cranes, etc. are installed with pulleys.ForceSingle fixed pulleyForceSingle movable pulleyEffortBlock and tackle systemTypes of Pulleys1. Single Fixed PulleyA pulley that doesn’t move up and down with load is called a single fixed pulley. It doesn’t multiply the effort applied but it is widely used because it changes the direction of effort applied to make our work easier.

166 NOVA Science Book 9 Modern Concept Science and TechnologyFact and ReasonThe velocity ratio of a single fixed pulley is always one.In the case of a single fixed pulley, the distance moved downward by the effort is equal to the distance moved upward by the load (i.e. Ed = Ld). So, Mathematically,VR = distance moved by effort (Ed)distance moved by load (Ld) = LDLD = 12. Single movable pulleyA pulley that moves up and down with load is called a single movable pulley. A single movable pulley is used to multiply force in modern elevators, weight lifting machines, etc.Fact and ReasonThe velocity ratio of a single movable pulley is always two.In the case of a single movable pulley, the distance moved by the effort is twice the distance moved by the load (i.e. Ed = 2Ld). So, the velocity ratio of a single movable pulley is always two.Mathematically,VR = distance moved by effort (Ed)distance moved by load (Ld) = 2LDLD = 2Memory NoteThe velocity ratio of single movable pulley = number of rope segments to support the load = twoDifferences between a single fixed pulley and a single movable pulleySingle fixed pulley Single movable pulley1. It doesn’t move up and down with a load.1. It moves up and down with a load.2. It changes the direction of effort but does not multiply force.2. It does not change the direction of effort, but it multiplies the force.3. Its velocity ratio (VR) is one. 3. Its velocity ratio (VR) is two.4. It works like a first class lever. 4. It works like a second class lever.

Modern Concept Science and Technology NOVA Science Book 9 167ActivityMeasure the weight of a 1 kg mass (i.e. load) by a spring balance. Use the spring balance at one end of the rope to lift the load with the help of a single fixed pulley, single movable pulley, and block and tackle system as shown in the given figures. Fill the data in the given table after your measurements and calculate the corresponding efficiencies of different types of pulleys. Analyse the data and write the conclusion that you draw from your results in different cases.S.N. Type of pulley VR Load (L) Effort (E) MA Efficiency (h)1. Single Fixed Pulley2. Single Movable Pulley3. Block and Tackle SystemSOLVED NUMERICAL- 8.1How much is the distance moved by the effort to lift the load by 2 m in the pulley shown in the given figure? Calculate the efficiency of the pulley.Solution,Here,Load (L) = 300 NEffort (E) = 200 NLoad distance (Ld.) = 2 mIn the case of a single movable pulley,Distance moved by effort (Ed) = 2 × Ld∴ Distance moved by effort (Ed) = 2 × 2 = 4 m According to the formula, Efficiency (h) = Output workInput work × 100%= Load × Load distance Effort × Effort distance × 100%Also, (h) = MAVR × 100%h = LE2 × 100%h = 3002002 × 100%(Since, VR of single movable pulley is 2.)h = 75%200 N Alternative method300 N

168 NOVA Science Book 9 Modern Concept Science and Technology or, Efficiency(h) = 300 × 2200 × 4 × 100% or, Efficiency(h) = 68 × 100% ∴ Efficiency (h) = 75%.The efficiency of the pulley shown in the given figure is 75 %.3. Block and Tackle SystemA combination of pulleys is called block. The arrangement of pair of blocks consisting of one or more pulleys is called a block and tackle system. It can multiply force as well as change the direction of force.Fact and ReasonA block and tackle system is usually used to lift or pull heavy loads in the easiest way.The block and tackle change the direction and multiply force at the same time. The fixed block changes the direction and the movable block magnifies the force. So, a block and tackle system is usually used to lift or pull heavy loads in the easiest way.Memory NoteThe velocity ratio of block and tackle system = the number of rope segments to support the load = number of the pulley. For the block and tackle system with two pulleys in the block and one pulley in the tackle, velocity ratio = number of pulleys = 3.SOLVED NUMERICAL - 8.2How much is the distance moved by the effort to lift the load by 2 m in the block and tackle system having 5 pulleys? If the efficiency of the pulley system is 75% then calculate the effort applied to lift the 3000 N load.Solution,Here, Load (L) = 3000 N Load distance (Ld.) = 2 mIn the case of a block and tackle system with 5 pulleys,Velocity ratio = number of pulleys = 5 fixed pulley blockfixed end of ropeslotted massesBlock and tackle systemmoving pulley blockA block and tackle with VR = 4loadspring balance reading the effort forceET TT T

Modern Concept Science and Technology NOVA Science Book 9 169 or, Velocity ratio = 5or,Effort distance Load distance = 5or, Ed = 5 × 2∴ Ed = 10 mThe efficiency of the block and tackle system (η) = 75%According to the formula,or, Efficiency (h) = MA VR × 100%or, 75% = LE5 × 100%or, 75% = 3000 E × 5 × 100%or, E = 3000 75 × 5 × 100%∴ E = 800 NThe effort required to lift the load by the given block and tackle system is 800 N.Wheel and AxleA system of two co-axial cylinders of different diameters which rotate together is called wheel and axle. The larger-diameter cylinder is called a wheel and the smaller-diameter cylinder is called an axle. There is frequent use of wheel and axle in our daily life. For example, door knob, tap knobs, screwdriver, etc. Wheel and axle can’t increase both the force and the speed at the same time. It can work either like a force or a speed multiplier.Fact and ReasonThe truck steering wheel is larger than a car steering wheel.A larger-diameter steering wheel in trucks multiplies force by more amount than a smaller-diameter steering wheel in cars. This makes it easy to control the movement of the front wheels of a heavily loaded truck through the steering linkage. So, the truck steering wheel is larger than a car steering wheel.WheelAxleEffort LoadWheel and axle

170 NOVA Science Book 9 Modern Concept Science and TechnologyFact and ReasonWheel and axle can’t increase both the force and the speed at the same time.A wheel and axle multiplies force when the force applied is on its wheel. On the other hand, if the force applied is on the axle of a wheel and axle then it increases the speed of work. So, the wheel and axle can’t increase both the force and the speed at the same time.MA, VR, and Efficiency of Wheel and AxleSimple Machine MA VR EfficiencyWheel and AxleWheelAxleEffort LoadMA = LE VR = Effort distanceLoad distanceWhen effort is applied from wheel,VR = (Circumference of wheel (2πR))(Circumference of axle (2πr))VR = Radius of wheel (R)Radius of axle (r)h = MAVR × 100%h = LERr× 100%h = L × rE × R × 100%SOLVED NUMERICAL- 8.3In a wheel and axle, the radius of the wheel is 30 cm and that of the axle is 10 cm. If a load of 600 N is lifted by applying an effort of 250 N, then calculate its MA, VR, and efficiency.Solution Here,Load (L) = 600 NEffort (E) = 250 NRadius of wheel (R) = 30 cm Radius of axle (r) = 10 cm Now,i. MA = LE = 600250 = 2.4ii. In the case of a wheel and axle, VR = Rr = 3010 = 3

Modern Concept Science and Technology NOVA Science Book 9 171iii. According to the formula,Efficiency (h) = MAVR × 100% or, h = 2.43 × 100% h = 80%The efficiency of the wheel and axle is 80%.3.2 Inclined PlaneAn inclined plane is a simple machine with a sloped surface. The sloped flat supporting surface with one end higher than the other, used for raising or lowering a load is called an inclined plane. It is also known as a ramp. For example, a staircase, a ramp used to load goods into trucks, a road winding uphill.Memory NoteInclined planes are very useful to make disabled friendly hospitals and houses.ActivityMeasure the weight (i.e., load, L) of a heavy toy car by a spring balance. Attach it to the spring balance and pull it over the inclined planes as shown in the given figures to calculate the values of effort applied (E). Fill the data in the given table after your measurements and calculate the corresponding efficiencies of the inclined planes. Analyse the data and write the conclusion that you draw from your results in different cases.S.N.Length of Inclined PlaneHeight of Inclined PlaneVR Load (L) Effort (E) MA Efficiency (η)1.2.3.1 m 0.5 m1.5 m 0.5 m2 m 0.5 m600 N400 N

172 NOVA Science Book 9 Modern Concept Science and TechnologyThe length of an inclined plane is always greater than its height so it can multiply effort.MA, VR, and Efficiency of Inclined PlaneSimple Machine MA VR EfficiencyWheel and Axle600 N 400 NMA = LE VR = Effort distanceLoad distanceWhen effort is applied from wheel,VR = Length of inclined plane (l)Height of inclined plane (h)VR = lhh = MAVR × 100%h = LElh× 100%h = L × hE × l × 100%SOLVED NUMERICAL - 8.4Study the given figure and calculate.i. MA ii. VR iii. EfficiencySolutionHere, Load (L) = 500 N Effort (E) = 200 N Load distance (Ld) = 1 m Effort distance (Ed) = 4 m Using formulai. MA = LE = 500200 = 2.5ii. VR = Effort distance Load distance = 41 = 4According to the formula,Also, (h) = MAVR × 100% h = 2.54 × 100% or, h = 62.5%.The efficiency of the pulley shown in the given figure is 62.5%.500 N200 N4 m1 m

Modern Concept Science and Technology NOVA Science Book 9 173ScrewThe figures shown alongside are showing the application of screws in our daily life. A screw is a simple machine with an inclined plane wrapped around a cylinder. It has a structure like a winding inclined plane. The line formed by the inclined plane is called a thread. The perpendicular distance between adjacent threads is called pitch.Memory NoteScrews and wedges are modified inclined planes.The velocity ratio of the screwWhile using a screw, when effort makes one complete turn, the resistance force moves a distance equal to the pitch. If ‘r’ is the length of the lever arm or that the top of the screw over which screw driver is fixed to rotate it, then effort distance is equal to the circumference.i.e. effort distance = 2πrIf, ‘d’ is the length of the pitch, theni.e. Load distance = dThe velocity ratio of the screw is given byVR = Effort distance Load distance = 2πrdWedgeA knife is an example of a wedge. It has a sharp cutting edge that looks like two slanted surfaces meeting at the edge to form a sharp structure. In the given figure, a knife is being used to cut potatoes. Cutting becomes easy with the knife because of the wedge shape of the blade. The very thin edge of the blade easily enters and cuts through the potato.Input forceoutput forceoutput Wedge force

174 NOVA Science Book 9 Modern Concept Science and TechnologyA wedge is a simple machine that consists of two inclined planes, giving it a thin end and a thick end. It is used to cut or split apart objects. It makes work easier by increasing the force applied to the object. Force is applied to the thick end of the wedge, and the sloping sides of the wedge apply force to the object for cutting it or splitting it apart.Fact and ReasonThe mechanical advantage of a wedge is greater than 1.A wedge applies more force to the object (output force) than the user applies to the wedge (input force), so the mechanical advantage of a wedge is greater than 1.The velocity ratio of wedgeIn the given figure, input force is applied to the head of the wedge. The sharp edge penetrates deep inside the substance to be cut. If ‘W’ is the width of the head of the wedge and ‘L’ is its length, then distance moved by effort is the length of the wedge, and distance moved by the load is the width of the head of the wedge. i. e.,effort distance = Lload distance = WThe velocity ratio of the wedge is given byVelocity ratio (VR) = Effort distance Load distance = LWSOLVED NUMERICAL- 8.5Find the velocity ratio of the wedge shown in the given figure. Solution:Given,Width of the inclined plane (W) = 10 cm Length of the inclined plane (L) = 30 cmThe velocity ratio of the wedge is given byVelocity ratio (VR) = Effort distance Load distance = LWor, Velocity ratio (VR) = 30 10 = 3Input forceWedgeWooden Plank1030Input forceWedgeWooden Plank

Modern Concept Science and Technology NOVA Science Book 9 175Compound MachineActivity 8.3Look at the given pictures of different machines. Discuss about the simple machines used in their construction and their role in performing work with the use of that machine.scissors stapler wheelbarrowSewing machine bicycle Fishing rodMost of the machines we use nowadays are compound in structure. A complex structured machine with two or more simple machines working together is called a compound machine. For example, clocks, bicycles, motorbikes, sewing machines, etc. Compound machines use different types of energy like electrical energy, chemical energy, etc. to work.1. Simple machine: The device which makes our work easier, faster, and more convenient is called a simple machine.2. Compound machine:A complex structured machine with two or more simple machines working together is called a compound machine.3. Load: Load is the resistance to be overcome or the weight being lifted by a simple machine.4. Load distance: The distance moved by the load in a simple machine is called load distance.5. Effort: Effort is the force applied directly to a simple machine to move the load or to do work.6. Effort distance: The distance moved by effort applied in a simple machine is called effort distance.Terms and terminologies

176 NOVA Science Book 9 Modern Concept Science and Technology7. Mechanical advantage (M.A.):The ratio of the load lifted to the effort applied in a simple machine is called mechanical advantage.8. Velocity Ratio (V.R.): The ratio of the distance moved by the effort to the distance moved by the load in a simple machine is called velocity ratio.9. Input work: Work done on a simple machine by a given effort is called input work.10. Output work: Work done by a simple machine on the load is called output work.11. Efficiency: The ratio of output work to input work in a simple machine expressed as a percentage is called efficiency.12. Practical machine: The machine which has friction is called a real or practical machine.13. Perfect simple machine: A hypothetical frictionless machine in which total input work is converted into output work without wastage of energy is called an ideal or a perfect simple machine.14. Pulley:The metallic or wooden circular disc having a groove along its rim and capable of rotating about an axis passing through its centre is called a pulley.15. Single fixed pulley: A pulley that doesn’t move up and down with load is called a single fixed pulley.16. Single movable pulley: A pulley that moves up and down with load is called a single movable pulley.17. Block and tackle: The arrangement of pair of blocks consisting of one or more pulleys is called a block and tackle system.18. Wheel and axle: A system of two co-axial cylinders of different diameters which rotate together is called wheel and axle.19. Inclined plane: The sloped flat supporting surface with one end higher than the other, used for raising or lowering a load is called an inclined plane.20. Wedge: A wedge is a simple machine that consists of two inclined planes, giving it a thin end and a thick end.21. Screw: A screw is a simple machine with an inclined plane wrapped around a cylinder.22. Pitch: The distance between adjacent threads is called pitch.Terms and terminologies

Modern Concept Science and Technology NOVA Science Book 9 177EXERCISESTEP 1 Multiple Choice Questions1. Choose the best answer from the given alternatives. a. Which one of the following is a set of inclined planes?i. Crane, steering, ladder ii. Ladder, slanted road, ramp iii. Pulley, screw, bicycle iv. Needle, axe, sickle b. Where is effort applied in a typical wheel and axle?i. On the wheel ii. On the axle iii. On the axis iv. On the fulcrum c. If the efficiency of a four-pulley system is 75%, calculate its mechanical advantage.i. 4 ii. 4 N iii. 3 iv. 3 Nd. Why is the mechanical advantage of a simple machine always less than its velocity ratio? i. V.R. is affected by friction. ii. M.A. is input work. iii. V.R. is output work. iv. M.A. is affected by friction. e. What is the formula for the efficiency of an inclined plane? i. h = L× lE × h × 100% ii. h = h × EL × l × 100%iii. h = L × hE × l × 100% iv. h = l × hE × L × 100%STEP 2 Very Short Answer Type Questions2. Define the following terms. (a) Load (b) Load arm (c) Effort (d) Effort arm (e) Mechanical advantage (f) Velocity ratio(g) Input work (h) Output work (i) Efficiency(j) Real machine (k) Perfect machine (l) Compound machine(m) Pulley (n) Single fixed pulley (o) Movable pulley (p) Combined pulley (q) Wheel and axle (r) Inclined plane

178 NOVA Science Book 9 Modern Concept Science and Technology3. Under what condition mechanical advantage of a machine will be less than one?4. How would you increase the mechanical advantage of a doorknob?5. Identify the type of pulley shown in the diagram. 6. It has a thread that spins around a big cylinder. What type of simple machine is it? 7. In which case, A or B, is the wheel and axle axe as a speed multiplier? Why? Effort is used in the wheel Wheel and Axle Effort is used in the axle. A BSTEP 3 Short Answer Type Questions8. Write any two differences between: (a) Effort distance and Load distance(b) Mechanical advantage and Velocity ratio (c) Input work and Output work (d) Real machine and Perfect machine (e) Fixed pulley and Movable pulley (f) Screw and Wedge 9. Give suitable reason.(a) Velocity ratio does not have a unit. (b) Efficiency of a machine is less than 100%. (c) The wheel and axle is called a continuous lever. (d) VR of the inclined plane is more than one. (e) Lubricants can increase the efficiency. 10. There is a simple machine on the well. Observe its structure. What is this simple machine? 11. The tools that have simple structures are called …… The combination of many …… makes compound machines. QuestionsWhat are the features and uses of the technology discussed in the given paragraph?

Modern Concept Science and Technology NOVA Science Book 9 17912. The adjacent figures show two inclined planes of the same height ‘h’. However, the lengths of the two planes are ‘2l’ and ‘3l’ respectively. Which inclined plane makes our work easier while lifting a load? Write with reason.STEP 4 Long Answer Type Questions13. Ramhari rides a bicycle to deliver food to his customers. The bicycle makes it easier and faster to travel. He frequently uses motor oil on the chain and joints of his bicycle.Questions(i) What type of machine is the bicycle?(ii) What types of simple machines are found in bicycles? (iii) What are the advantages of using motor oil on the chain and joints of the bicycle? 14. Observe the given characteristics and answer the following questions.Pulley A Pulley B Pulley COne of its discs cannot change position while others can.It has only one disc that can travel in the rope.It has only one disc that is fixed in the support. Questions(i) What type of pulley is A? (ii) Mention the velocity ratio of pulley B. (iii) What are the uses of pulley C? (iv) Why do people use pulley C even though it cannot make work easy? 15. Study the given diagram and answer the following questions. (i) What is the velocity ratio of the single pulley system shown? Write with reason.(ii) What is the velocity ratio of the two-pulley system? Write with reason.(iii) If the efficiency of the twopulley system is 75%, find the effort required to lift a load of 500 N with its help. h h2 l 3 lL Efixed pulleyLEfixed pulleymovable pulley

180 NOVA Science Book 9 Modern Concept Science and TechnologyNumerical Problems1. A load is lifted up with the help of a pulley as shown in the given figure. Calculate the MA and efficiency of the pulley. How much percentage of the energy is wasted while lifting the load? [Ans: MA = 0.8, 80%, 20%]2. The mechanical advantage of a machine is 5. Its efficiency is 80%. It is used to lift a load of 500 N to a height of 20 m. Calculate: i. the effort required ii. the effort distanceiii. the work done on the machine iv. the output work [Ans: i. 100 N ii. 125 m iii. 12500 J iv. 10000 J]3. A block and a tackle system have five pulleys. If an effort of 1,000 N is required to lift a load of 4,500 N, find MA, VR, and efficiency. [Ans: 4.5, 5, 90%]4. Find the MA, VR, and efficiency of the wheel and axle shown in the given figure. [Ans: MA = 2.5, VR = 5, h = 50%]5. A wedge having a thickness of 6 cm and a length of 20 cm is used to split a wooden log. If the amount of force applied is 500 N and the resistance overcome is 1,400 N then find the value of MA, VR, and efficiency. [Ans: 2.8, 3.33, 84%]6. A load is lifted by using an inclined plane as shown in the given figure. Calculate MA, VR, and efficiency. What should be the length of the plane to pull the same load with the effort of 25 N remaining the efficiency constant? [Ans: 2, 2.5, 80%, 10 m]MCQ a b c d e Answer ii i iii iv iii Make a model of a single fixed pulley on a well. PROJECT WORK80 N100 N50 NE = 50 N5 m2 mL = 100 N

Modern Concept Science and Technology NOVA Science Book 9 181Dr. Ramesh Kumar Maskey is a scientist of the Nepal Academy of Science and Technology. He is an engineer. His research is related to renewable energy technology, small hydropower, water resources management, and hydraulic structures. He was involved in the Arun-III hydroelectric power project. He was an educator at Kathmandu University. Dr. Ramesh Kumar MaskeyInspiring Nepalese ResearcherGundruk, Sinki, Masyaura, and Sukuti are local foods in Nepal. These are sun-dried foods. These foods last for many months. Nepalese have been using solar energy for drying grains for ages. Lately, many modern technologies have been developed and are growing popular in Nepal. These technologies harvest solar energy and make our lives easier. For example, a solar water heater is the most common device used to warm water. Questionsi. What is solar energy?ii. What are the natural uses of solar energy?iii. Enlist any two technologies designed to harvest solar energy.Fig. : Gundruk WARM UP ACTIVITYIntroductionEnergy is the ability to do work. Whatever work is done, some energy has to be spent. Living beings as well as machines need the energy to perform work. There is no work accomplished without energy. When we walk, our muscular energy is used up. To run vehicles, fossil fuel is used as a source of energy. There is increased use of energy sources that can replace fossil fuels to prevent the future scarcity of energy resources. For example, biogas is a biofuel to cook food. The use of biomass briquettes can replace the use of coal for heating purposes. While ENERGYUNITESTIMATED TEACHING PERIODS9TH PR6 2

182 NOVA Science Book 9 Modern Concept Science and Technologyperforming a work by using energy, the energy does not vanish rather it changes into some other forms of energy. Energy can neither be created nor destroyed, but it can be transformed from one form to another. This is called the principle of conservation of energy.Source of energyActivityWhat sources of energy do people use in your locality? Make a list of energy sources and classify them into two categories as the source that can provide energy continuously for a long time and the source that have limited reserve on the earth which gets depleted on its continuous use.Energy resources on the earth can be classified as non-renewable sources andrenewable sources.Non-renewable sources of energySome energy sources cannot be generated in a short period. They cannot be used again and again. The energy sources which occur in limited and exhaustible amounts are called non-renewable energy sources. For example, coal, petroleum, natural gas, nuclear sources, etc. Such sources are if once used up, can not be renewed for millions of years. But some non-renewable resources such as metals can be used again and again. i.e., they can be recycled.Renewable Energy SourcesSome of the energy sources can be replenished in a short period. The sources of energy, which are being produced continuously in nature and are inexhaustible are called renewable energy sources. For example, hydropower, wind energy, wood, charcoal, biomass, etc. Oxygen is a renewable source of energy because it is replaced in the atmosphere as plants release oxygen during photosynthesis. But if we use some renewable sources of energy faster than they are renewed, they are exhaustible too. For example, nowadays the groundwater is being exhausted from some locations due to its excessive use.Solar energyThe sun is the closest star to the earth. Its average distance from the earth is 1.5 × 108 km. Its mass is about 2 × 1030 kg. The core temperature of the sun is about 15,000,000 K. Whereas the surface temperature is about 5778 K. It provides an adequate amount of heat and light energy for life to exist on the earth. 3.8 × 1026J/s energy gets released from the sun. More than half of the incident energy from the sun is either reflected back to space or absorbed in the atmosphere. As solar

Modern Concept Science and Technology NOVA Science Book 9 183energy passes through the atmosphere, most of the ultraviolet and gamma rays are absorbed by the atmosphere. Such energy does not fall equally in all parts of the earth. On average, 1.4 kW of solar energy falls per square meter on the earth surface. A part of this solar energy is absorbed by the landmass, the water bodies and plants. Such energy consumed causes the phenomena like wind, storms, rainfall, snowfall, etc.Thermonuclear Fusion: Source of the Solar EnergyThe sun obtains its energy through a process of nuclear fusion. It is composed mostly of the gases like hydrogen and helium. The core of the sun is at a high temperature of about 15 million degrees Celsius. Hydrogen ions (H+) are found at such a high temperature when the electrons of hydrogen atoms separate from the atom. There is high repulsion between hydrogen ions i.e. protons. The extremely high pressure caused by the gravitational pull brings them closer forming helium atoms. The process of formation of helium atoms from hydrogen atoms in presence of high temperature and pressure in the stars like the sun is called thermonuclear fusion. During this process, a huge amount of energy gets released in the form of heat and light. It occurs in the following three different steps.i. Two protons combine to form a deuterium (1H2) along with a positron i.e. positive electron (1e0)1H1 + 1H1→1H2 + 1e0 + energyii. The deuterium thus formed combines with another proton to form a light helium atom (1He3).1H2 + 2H1→ 2He3 + ϒ – radiationiii. Finally the two light helium atoms combine together to form a stable helium atom (2He4) along with two protons.2He3+ 2He3→ 2He4 + 1H1 + 1H1 + energy In short42H1 → 2He4 + 21e0 + energyMemory NoteIsotopes are the atoms of an element having the same number of protons but a different number of neutrons. Thus, the isotopes have the same atomic number but a different mass number. For example, Protium (1H1), Deuterium (1H2) and tritium (1H3) are the isotopes of hydrogen. In the notation 1H2, 1 stand for the atomic number and 2 stands for atomic mass (1 proton + 1 neutron).

184 NOVA Science Book 9 Modern Concept Science and TechnologyConditions Suitable for Thermonuclear Fusion in the Suni. Abundant hydrogen: There is a sufficient amount of hydrogen in the sunwhich continues the thermonuclear fusion.ii. High temperature: The high temperature in the sun forms free protons in the plasma state.iii. High pressure: Pressure squeezes the atoms together for their combination.Einstein’s mass-energy relationEinstein’s mass-energy relation is used to calculate the energy released from the fraction of mass that gets lost in each step of the thermonuclear fusion. The energy released from the mass lost in a nuclear reaction is given by Einstein’s massenergy relation; E = mc2. Where ‘m’ stands for the mass lost and ‘c’ is the speed of light (i.e. 3 × 108 m/s).For example, if 0.5 g of mass is lost during the nuclear reaction, the energy released is given by E = mc2 = 5 × 10-4 × ( 3 × 108 )2 = 5 × 10-4 × 9 × 1016 = 4.5 × 1013 J. Thus, a huge amount of energy gets released from a nuclear reaction.The sun as an ultimate source of energyThe sun is the main source of all forms of energy. It gives us heat and light energy. The sun is considered the ultimate source of energy because the different forms of energy are directly or indirectly obtained from the sun. Following are some examples:i. The water cycle is also known as the hydrological cycle. This cycle includes precipitation, evaporation, condensation, etc. This happens due to the Sun’s heat. The heat from the sun melts snow and ice blocks and water fills in rivers. Water molecules from lakes, rivers, streams, reservoirs and the sea get heated up by the sun and change into a vapour that rises into the air. Condensation of such water vapours forms cloud and rainfall occurs.

Modern Concept Science and Technology NOVA Science Book 9 185If the water vapours are frozen, they become snow. Finally, the water in rivers is collected in big dams to generate electricity. Thus, hydroelectricity is indirectly derived from the sun.ii. A small portion of the sun’s energy reaching the earth is absorbed by green plants through the process of photosynthesis. In this process, carbon dioxide and water are converted into carbohydrates. The sun’s energy is then converted into chemical energy and stored in various parts of the plants. The carbohydrates are consumed as food by the animals. Thus, the energy which we obtain from food is derived from the sun.iii. The energy in fossils fuels like coal, petrol, diesel, natural gas, etc. originally comes from the sun. They are formed by the fossilization of ancient plants and animals which captured solar energy through photosynthesis. Weburn fossil fuels to release the energy that ancient plants captured from the sun. Thus, fossil fuel energy is derived from the sun.iv. Biomass fuels are obtained from once-living sources. Wood, vegetation, crop residues, garbage, etc. are examples of biomass. Plants store solar energy during the process of photosynthesis. The energy from the plants is transferred to the animals. Thus, the energy which we obtain from biomass is actually derived from the sun.v. Sun’s rays heat the air around the earth. But the energy from the sun does not fall uniformly at all parts of the earth. Air gets heated unequally and air pressure variation occurs. Then air blows from the region of high pressure to the region of low pressure. Thus, wind energy is also an outcome of solar energy.Solar energy harvesting technologiesActivityLook at the pictures showing the traditional method of solar energy harvesting and the corresponding modern method.drying gundruk in the open air drying gundruk in the solar dryer

186 NOVA Science Book 9 Modern Concept Science and TechnologyWhat other kind of solar energy harvesting methods have you seen in your locality?We can see solar panels fixed on some of the residential rooftops in our locality. People use solar panels, solar water heaters, solar dryers, etc. The use of such tools is solar energy harvesting technology. Solar energy harvesting is the process of capturing and storing solar energy which is radiated from the sun. Following are some of the solar energy harvesting technologies.Photovoltaic Solar PanelsA solar cell or photovoltaic (PV) cell is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect. Several photovoltaic cells are connected together to make a solar panel. The solar panel is an assembly of photovoltaic cells mounted in a framework for installation. Solar panels use the sun’s power to create a flow of electricity. The size of a solar panel ranges in size from a few square centimetres to a few square metres. The use of solar panels is the most widely adopted method of harvesting solar energy.Photovoltaic cell Solar panel fixed on the rooftopSunlightNegative electrodePositive electrodeElectric currentEach PV solar cell is made up of semiconductor material. The structure’s two thin semiconductor wafers are placed on top of each other. When light falls upon such a structure then it creates a flow of electricity through two terminals. The electricity is compounded into a whole panel of solar cells and then into a vast PV panel array. PV solar arrays produce direct current (DC).Fact and ReasonWe need an inverter to run devices connected to our domestic circuit through electricity generated from the solar panel, why?The devices connected in our domestic circuit run from alternating current (AC). However, the electricity generated from the solar panel is DC. An inverter converts DC into AC. So, the DC from the solar panel must be converted to AC by using an inverter to run appliances connected to our domestic circuit.

Modern Concept Science and Technology NOVA Science Book 9 187Photovoltaic cells are used in different devices like solar lamps, solar streetlamps, etc.Solar LampA solar lamp or solar lantern is a lighting system composed of a LED lamp, solar panels, battery and charge controller. There may also be an inverter in a solar lamp if it runs from both AC and DC. The lamp operates on electricity from batteries, charged through the use of solar panels i.e., solar photovoltaic panels. Solar-powered lamps help in achieving energy independence by utilizing the power of the sun.Solar street lampsSolar street lights are raised light sources which are powered by solar panels integrated into the pole. The solar panelscharge a rechargeable battery, which powers a fluorescent lamp or Light Emitting Diode (LED) lamp during the night. Solar street lights consist of four main parts: solar panel, lighting fixture, rechargeable battery, and pole.The solar panel converts solar energy into electricity. This electricity generated is used to charge batteries and to power the lamps. Charge controllers are used to control the charging of the batteries. The main functions of charge controllers are to prevent over-charging of batteries from solar panels, over-discharging of batteries to the load and to control the functionalities of the load. LEDs are usually used as the lighting source of modern solar street lights. A rechargeable battery stores the electricity generated by the solar panel during the day and provides energy to the fixture during the night. A strong pole is necessary to support all components fixtures, panels, and sometimes batteries. In the case of newer designs, PV panels and all electronics are integrated with the pole itself.Memory NoteLEDs used in modern solar street lights provide much higher luminosity with lower energy consumption.Solar lampSolar street lamps

188 NOVA Science Book 9 Modern Concept Science and TechnologySolar cookerA solar cooker is a device that uses the energy of direct sunlight to heat, cook or pasteurize drinks and other food materials. It has a curved mirror to converge solar radiation at the pot used for cooking. The cooking pot used in the solar cooker has a black outer surface that absorbs heat radiations.Solar cooker Working principle of solar cookerFact and ReasonThe outer surface of the cooking pot used in solar cookers is black, why? Black colour effectively absorbs infrared radiations. So, the outer surface of the cooking pot in the solar cooker is made black to absorb solar radiation for effective heating.Solar water heaterA solar water heater is a device that captures sunlight to heat water. Commonly solar water heater is used to heat water for bathroom purposes. The simplest version of a solar water heater system uses a pump to circulate cool water through a black body panel. The water is continually circulated through a loop. Some systems do not have a pump system. In such a system, the warmer water ‘floats’ and the colder water sinks that creates a thermosiphon. Thesesystems require the storage tank to be above the solar absorption source as in the case of a vacuum tube solar water heater.Solar water heater

Modern Concept Science and Technology NOVA Science Book 9 189Fact and ReasonVacuum tube solar water heaters are good for water heating purposes in winter, why? The solar radiation intensity is low in winter. In a vacuum tube solar water heater, minimal amounts of thermal energy escape the vacuum tube. It allows nearly all radiant energy to be converted into thermal energy. So, vacuum tube solar water heaters are significantly more efficient at heating water during cold months.Solar dryerTraditionally, food grains, vegetables, etc. are kept in the sun to make them dry. This takes more time. The use of a solar dryer to make foods dry saves time. A solar dryer is a device that uses solar energy to dry substances, especially vegetables, fruits, herbal products, spices, etc. The temperature of the air inside the drier is more than that of the air outside it. It can replace the traditional method of drying foods in the sun. Food is protected from flies, other insects, rain and dust. The quality of food remains high in terms of colour, health, and nutrients. So, the use of a solar dryer avoids the possibility of contamination when drying food in the external environment.ActivityUse locally available resources to make models of each solar cooker, solar water heater and solar dryer.Biomass energyBiomass is the material that comes from living organisms such as plants and animals. The most common biomass materials used for energy are plants, wood, straw, sawdust, agricultural waste, etc. The energy from biomass can be transformed into usable energy through direct and indirect means. Biomass can be burned to create heat directly. Sometimes biomass is processed into biofuel indirectly like alcohol. The energy released from biomass through combustion or other chemical process is called biomass energy.Fact and ReasonBiomass is a renewable source of energy.Plants and animals will always exist as long as the conditions are suitable for life on the earth. As long as we plant trees and crops, we will have resources. Biomass supplies are not limited. It can be obtained continuously on the earth. So, biomass is a renewable energy source.Solar dryer

190 NOVA Science Book 9 Modern Concept Science and TechnologyBiogasThe biomass can be converted into combustible gas i.e. biogas in a biogas plant. Biogas is a mixture of gases like methane (CH4), carbon dioxide (CO2), hydrogen (H2) and hydrogen sulphide (H2S). The major constituent of biogas is methane. A biogas plant is a physical installation to produce biogas from biomass. It is built either of cement-concrete or brick-walled.In a biogas plant, the feed is fed into the system from the mixing tank. It has a mixing fan to make a slurry from animal dung and water. There is a pipe from the mixing tank to the digestive tank to send the feed into the digestive tank. A digestive tank is a brick-walled underground tank with a dome-shaped roof. It is an airtight tank, where the feed and water will stay for some time and anaerobic decomposition generates gas. The biogas generated gets stored in a dome. With an increase in pressure of the gas inside the dome, it pushes the digested material out of the tank into the outlet chamber. There is a pipe with a valve at the top of the dome as a gas outlet. Gas generated is supplied through an outlet valve. Biogas from the biogas plant can be supplied through pipes for cooking and lighting. The outlet chamber is for taking out the spent slurry after completion of gas generation from it.Memory NoteBiogas can be used as cooking fuel, lighting fuel, to generate electricity, and fuel for the combustion engine.Organic matter rich substances are used as input material for biogas production. Animal wastes like cattle dung, urine, goat and poultry droppings, etc. Similarly, human wastes and kitchen wastes, agricultural wastes, etc. can be used as input material for biogas production. In the village area of our country, the main input material for biogas production is cattle dung.Fact and ReasonBiogas is one of the suitable sources of energy for village areas in Nepal.In the village area, many people are engaged in farming.The raw materials like animal dung, plant wastages, etc. are easily available.It can be used for cooking food, lighting, etc. So biogas is one of the suitable sources of energy for village areas in Nepal.

Modern Concept Science and Technology NOVA Science Book 9 191Advantages of Biogasi. It produces more heat when burnt.ii. The use of biogas as cooking fuel replaces the use of firewood. So, it helps to control deforestation.iii. It is a non-polluting fuel as it does not produce smoke. So, it helps in controlling air pollution.iv. The spent dung slurry, left after the extraction of biogas, is rich in nitrogen and phosphorus compounds. It provides nutrient-rich manure for plants.v. Biogas can also be used in thermal power plant to produce electricity for lighting purposes.Memory NoteThe spent dung slurry, left after the extraction of biogas, is rich in nitrogen and phosphorus compounds and hence forms good manure.Limitation of biogasThere are some limitations associated with the biogas plant. The initial cost of installation of the plant is high but it’s a cheap energy source for long term use. In winter, the rate of gas production slows down. In the case of a smaller number of cattle owned by a farmer, animal dung is insufficient to feed a biogas plant. Biogas plant construction occupies more space. So, it is not possible to construct biogas plants anywhere in cities.Biomass briquetteBriquettes are solid fuels often used for domestic purposes in developing countries. They are used for heating purposes in industries too. Briquettes are formed by the compaction of solid material. A briquette is a compressed block of coal dust or other combustible biomass material such as charcoal, sawdust, wood chips, peat, or paper used for fuel and kindling to start a fire.Memory NoteCompaction or densification of briquettes increases the heating value per unit volume.Types of biomass briquettesCarbonized or charcoal briquettes and noncarbonized biomass briquettes are the two types of biomass briquettes.

192 NOVA Science Book 9 Modern Concept Science and TechnologyCharcoal briquettespowdered charcoal powdered clay mouldCollect powdered charcoal, powdered clay (sticky soil), and a mould as shown in the given figure. Measure each powdered charcoal and sticky clay to mix them in a ratio of 3:1 to make a paste. Press that paste in the mould. Take it out and let it become dry for 2 to 4 days.carbon rich material burning in low oxygen sticky clay briquetteA charcoal briquette is a compressed block of charcoal. It is produced by burning a carbon-rich material such as wood in a low-oxygen atmosphere and then mixing it with another binder. Commonly sticky clay is used as a binder while making charcoal briquettes. They are not actual charcoal lumps, but a combination of charcoal and other ingredients moulded into easy-to-light lumps.We need to collect raw materials to make carbonized briquettes at first. Raw materials like litter, fallen branches of trees, straw, etc. Then we need to let them dry. Dry matter is then burnt in a drum or a pit to make charcoal. Powdered charcoal is mixed with fine clay in a ratio of 3:1. This mixture is converted into a paste by adding water. That paste is pressed in a mould to give the shape of a briquette. Finally, the briquette becomes ready for packing after drying for 2 to 4 days.Beehive charcoal briquette banana peel briquettes coconut charcoal briquettes

Modern Concept Science and Technology NOVA Science Book 9 193Biomass briquettesMemory NoteAnimal Dung Briquettes (Guitha)In the village area of our country, farmers press animal dung by their hand and let that dry in the sun to make animal dung briquettes.Biomass briquettes are a biofuel substitute for coal and charcoal. A biomass briquette is compressed biomass by using a moulder and compressor. It is prepared by densification of woody biomass, leafy biomass, and agricultural residues. The agricultural waste like groundnut shells, castor seed shells, almond shells, coconut shells, rice husk, cotton stalks, sunflower stalk, pine needles, coffee husk, and other waste from forest like fallen leaves, tree bark, sawdust, jute waste, etc. can be used to make biomass briquettes. Biomass briquettes are given different shapes by using moulders.sawdust briquettes rice husk briquettes paper briquettesMemory NoteIn Nepal, the first commercial production plant ‘Nepal Bio-Extruder Industry Pvt. Ltd.’ was established in 1982 in Thapathali, Kathmandu with an annual production capacity of 900 metric tons. Screw press technology to make briquettes was introduced by Japan in our country in 1986 AD.There are different technologies for pressing the biomass briquettes.

194 NOVA Science Book 9 Modern Concept Science and Technologypiston press briquetting technologyscrew press briquetting technologyroller press briquetting technologyUse of biomass briquetteThe use of biomass briquettes can replace fuels like diesel, kerosene, lignite, coal, firewood, etc. In our country where a huge amount of agro-residues is available, this technology can handle a wide range of biomass to give good quality briquettes. Biomass briquettes can be used for the following purposes:i. It is used for room heating purposes.ii. It is used as fuel for cooking purposes in the kitchen, picnic spots, etc.iii. People use briquettes for warming the children and newly delivered mothers.iv. It can be used instead of wood and loose biomass in small scale industries like rubber industries, leather processing units, brick kilns, etc.How to use a briquette?To use a briquette, we need to ignite one end of a briquette until it turns red.Then it is transferred into its stove which is made up of ceramic, iron or steel. The burnt part of the briquette is kept downward.Advantages of biomass briquetteThe use of firewood can be replaced with the use of biomass briquettes. So, the use of biomass reduces deforestation. Simple skills and low expenditure need for briquette production. It can be a good source of income by commercial production. It reduces the energy crisis problem. There are several advantages associated with the use of biomass briquettes:i. It is a cheap and readily available renewable source of energy.ii. It is much cleaner to handle than charcoal or coal.iii. It reduces air pollution and helps to conserve the environment.iv. It replaces the use of fossil fuels like kerosene, LPG, etc. and traditionalsources of energy like firewood, coal, and dung-cake.

Modern Concept Science and Technology NOVA Science Book 9 195v. Ash after complete combustion of a briquette can be used in gardens and fields.vi. Loose biomass causes a problem in handling, transportation and storage. Briquettes are easy to handle and eliminate problems of transportation and storage of loose biomass.Limitation of biomass briquetteThere are some limitations associated with the use of biomass briquettes. It requires a huge investment for its initial production. There is a high energy requirement for the production of biomass briquettes. In the rainy season, the drying process needs another heat source other than the sun. Biomass briquettes must be stored in a waterproof storage area otherwise the briquettes will not burn when lit. The quality of the raw materials and wearing of the mould piston, and screw are frequent operational problems associated with briquetting technology. Doors and windows must be open while using the briquette otherwise, it may suffocate us.Use of alternative sources of energy in NepalThe present rate of fossil fuel consumption is high. This will bring energy crisis in the near future. The shortage of sources of energy for daily use is called energy crisis. To avoid this, we need to find sources of energy that replace fossil fuels. The sources of energy that are available in nature and can be used instead of non-renewable energy sources are called alternative energy sources. Renewable sources of energy are also called alternative sources of energy.Nepal has a great potential for renewable energy resources. Hydropower, solar energy, biomass, biogas, and wind energy are all sources of renewable energy in Nepal. Traditionally, people have been using biomass energy resources. To work in the field of alternative sources of energy, Nepal established a semiautonomous agency called the Alternative Energy Promotion Centre (AEPC) in 1996. It worked in the field of solar energy, mini/micro hydropower projects, biogas plants, improvement of cooking stoves, biomass energy etc.Solar PV technologies, solar thermal energy technologies (solar dryer, solar cooker, solar heater), biomass technologies, wind energy technology, biogas technologies (household biogas, urban household biogas, large biogas), mini/ micro hydropower technologies are in the implementation phase in Nepal. Several solar power stations like Nuwakot solar power stations have got installed in different parts of Nepal.

196 NOVA Science Book 9 Modern Concept Science and Technology1.5 MW Nuwakot solar power stationwind-solar hybrid power station at Hariharpur, sindhuliWind energy in NepalThe energy received from the blowing air across the earth is called wind energy. Strong wind regions of Nepal have a high potential for the generation of electricity from windmills. A wind power station is established in Hariharpur of Sindhuli district.Solar and biogas in NepalFarmers in Nepal use solar dryers to store vegetables and fruits during the harvest season. If such products are not stored properly, they are more likely to rot without consumption. Many people in the village area have installed biogas plants. In city areas, a modified biogas plant made from plastic tanks is in use to generate biogas from biodegradable kitchen wastage. Use of solar water heater is also common in city areas as well as in some of the village areas too.Hydroelectricity in NepalHydroelectricity is the best alternative source of energy in Nepal. To generate hydroelectricity at a hydropower plant, water collected in a dam is allowed to pass through a tunnel. It converts the potential energy of water stored in a dam into kinetic energy. This energy can be used to rotate turbines connected with a generator. The kinetic energy of the flowing water is converted into the kinetic energy of the armature of a generator connected to the turbine. The electrical energy generated by rotating turbines connected to the generators with the help of moving water is called hydroelectricity. A hydroelectricity generating station that utilizes the potential energy of water at a high level is known as a hydroelectric power plant.